According to previously unpublished information revealed in response to requests made under the Freedom of Information Act, convoys transporting defence nuclear materials and warheads were involved in 24 'operational incidents' and 19 'engineering incidents' over the period January 2013 to July 2016 (copies of incident logs available to download at the end of this page).

Over this period the convoy was involved in three minor collisions: twice in May 2013, when two convoy vehicles collided with each other and when a convoy escort vehicle collided with a parked civilian vehicle, and again in January 2014, when an escort vehicle collided with a car at a Ministry of Defence (MoD) base during a rest stop.

In September 2015 one of the trucks which transports nuclear weapons lost power and broke down soon after leaving a military site, and convoy escort vehicles twice broke down and were declared unserviceable during convoy journeys in November 2013 and July 2015. Adverse weather affected convoy journeys in November 2013, forcing a route change, and in January 2014, when a rolling police blockade was set up to safeguard the convoy during snowy conditions, and the convoy was stopped by protesters on three occasions.

The new revelations bring the total number of reported safety incidents affecting the nuclear convoy since 2000 to 180. This is in addition to eight accidents which are known to have taken place between 1960 and 1991, the most serious of which occurred in January 1987 when a convoy vehicle carrying nuclear warheads skidded and overturned on an icy road in Wiltshire.

The report lists a series of credible accident scenarios that could trigger fires, explosions or a breach of containment, resulting in the release of plutonium and other radioactive materials from warheads. Evidence cited from an MoD report suggests that in extreme circumstances an accident could even trigger an “inadvertent yield” - a nuclear reaction leading to a large-scale release of radiation short of a full nuclear explosion. A terrorist attack on a nuclear convoy, according to the MoD, could cause “considerable loss of life and severe disruption both to the British people's way of life and to the UK's ability to function effectively as a sovereign state”.

The report simulates the results of an accident involving a nuclear weapon in five places through which the warhead convoy has travelled: Birmingham, Preston, Wetherby, Newcastle and Glasgow. In each case the people, hospitals, schools, universities, roads, railway stations and airports that could be contaminated and disrupted are identified, assuming that an accident would spread contamination up to ten kilometres from the scene of the crash, depending on which way the wind was blowing.

In Birmingham, for example, a nuclear convoy crash on the M6 at Spaghetti Junction near the city could put more than 1.3 million people at risk of radioactive contamination. Within a ten-kilometre radius there are over 400 schools, 38 railway stations and 18 hospitals that could be disrupted.

The report quotes independent nuclear engineer John Large as warning that a multiple crash and fire involving a warhead carrier would pose a significant – and plausible – risk to the public. “The inclusion of a flammable chemical tanker in the pile-up would add to the ferocity and, particularly if the incident occurred in a longish bridge underpass or similar, fire temperatures would be very demanding on the containment of the warhead carriers,” he said.

If the containment is breached, high explosives could catch fire or explode, he warned. “Once that happens then the enriched uranium and plutonium components will also be consumed by fire and, without effective containment, liberate some very fine plutonium dioxide particles.” The consequences of this would be very hard to mitigate and very long lasting, potentially contaminating significant areas of land and posing long term health impacts.

The report states that although emergency exercises run by the MoD rehearse disaster scenarios in which multiple crashes lead to fires, explosions and the spread of radioactive contamination over cities, post-mortem reports from six exercises reveal that the MoD and the emergency services would have serious difficulties dealing with such disasters. Post-mortems “make the same points year after year”, because many of the same problems keep recurring, suggesting that “lessons are not learnt”, and that “issues with delays, communications and co-ordination are rediscovered every time”, which “does not bode well should there ever be a serious accident”.